Contact lenses are ophthalmic lenses worn on the anterior cornea that are widely used for correcting many different types of vision deficiencies. These include defects such as near-sightedness (myopia) and far-sightedness (hypermetropia), astigmatism, and defects in near range vision usually associated with aging (presbyopia). A typical single vision contact lens has a real or virtual focus, which is the point at which parallel rays of light focus when the lens is placed perpendicular to the parallel rays, and an optical axis, which is an imaginary line drawn from the focus to the center of the optical zone of the lens. A posterior surface of the contact lens fits against the cornea and an opposite anterior surface has an optical zone that refracts light to correct vision. In the case of a typical spherical lens, the optical zone has a single radius of curvature, whereas the distance from any point on the optical zone to a point on the optical axis referred to as the center of curvature.
The optical zone is typically at the central section of the contact lens that corrects the refractive error of the wearer.
A typical human eye, as a result of the optical characteristics of the cornea and crystal lens, inherently exhibits an increasing amount of spherical aberration as the diameter of the pupil expands. Typically, the spherical aberration, of an adult, is about one diopter for a 6 mm diameter pupil, while the spherical aberration is slightly less than two diopters for an 8 mm pupil, regardless of the eye's sphero-cylindrical manifest refraction. Spherical aberration typically results in degraded night vision—when the pupils are dilated. FIG. 1A is a diagram 10 showing the power of lenses designed with spherical or toric surfaces for +6 diopters 12, 0 diopters 14 and −10 diopters 16. The variation in power across the optical zone, or pupil, is the spherical aberration of the lens. The dashed line 14 depicts the nominal amount of spherical aberration of the eye for an individual with a plano refraction.
Individuals including computer users or individuals at the onset of presbyopia require an intermediate corrective power for viewing objects, such as computer screens, at a range of about two to three feet. Generally, light from a computer monitor causes the diameter of the pupil to contract (myosis). While there exist contact lenses that provide intermediate correction, having to change back and forth between normal lenses and intermediate lenses is awkward for the user. Intermediate mono-vision is not well tolerated by most individuals.
Therefore, there is a need for a contact lens that corrects the spherical aberration of the eye.
There is also a need for a contact lens that provides intermediate correction under certain circumstances, but that also provides distance vision correction that is not compromise.